For growing a monocrystal by a CZ (Czochralski) method, so-called codoping has been performed in which a primary dopant such as red phosphorus (P) or arsenic (As) that is solid at normal temperature and is evaporated near a surface of a semiconductor melt is injected together with a secondary dopant such as germanium that is solid at normal temperature and is liquefied near the surface of the semiconductor melt.
For codoping, the secondary dopant is injected into the semiconductor melt and then dopant gas generated by evaporation of the primary dopant is squirted onto the semiconductor melt.
However, when the secondary dopant is directly dropped into the semiconductor melt, the semiconductor melt scatters due to the drop of the secondary dopant, and foulings on a chamber or a furnace are dropped off during pull-up, which hampers monocystallization.
Thus, Patent Document 1 has suggested that a low-melting-point dopant as a secondary dopant is loaded into a low-melting-point-dopant injection tube which has a side wall and an upper portion hermetically sealed and a grid-like net formed on a lower portion, and the low-melting-point-dopant injection tube is soaked in a semiconductor melt, so that the low-melting-point dopant is melted by heat of the semiconductor melt and mixed with the semiconductor melt (for example, see Patent Document 1).    Patent Document 1: JP-A-2004-137140